The radio access scheme selected for Long Term Evolution, LTE supports event triggered downlink measurements based on Reference Signal Received Power, RSRP, and Reference Signal Received Quality, RSRQ. The typical handover evaluation for coverage triggered handover used today is downlink measurements performed by the wireless device and using event triggered measurement reporting. The serving network node (also referred to as the source network node) that receives the measurement reports from the wireless device initiate handover preparation and sends a handover request to a target network node and indicate the strongest reported cell as target cell. A network node may be associated with one or more cells each being a coverage area of the network node.
For inter frequency handovers, the cell of the target network node may be the best reported cell and good enough in downlink to be chosen. Handover oscillations are avoided by making sure that target is a couple dB better than the cell of the serving network node or good enough so no new Inter-frequency-handover is triggered when the wireless device arrives to target cell. If the uplink conditions between cells are roughly the same (no cell is disturbed significantly more in uplink than another cell) and the cell sizes are the same on one frequency layer, the method is typically enough for appropriate handover decisions. The method may be adjusted by using frequency offset and/or cell individual offset to compensate in general for different cell sizes and for different uplink conditions.
However, if frequency offset or cell individual offset is used those offsets need typically be semi stationary set and need to have rather large margins to avoid handover oscillations or moving to a cell where the uplink is not good.